不同土壤分類版本對於基樁軸向承載力之影響

Abstract

離岸工程普遍利用圓錐貫入試驗獲取土壤參數，因此CPT的數據常被用來作為離岸工程的土壤分類方法或基樁軸向承載力評估之研究參數。然而，基於CPT的土壤分類結果隨著不同的分類版本而不盡相同，且相對應的基樁承載力也有顯著的變化。本研究利用台灣建築物基礎構造設計規範 (DCSBF-SM法與DCSBF-CPT法)、ICP法、UWA法和UCM法分析基樁軸向承載力，以及根據台灣電力公司離岸風力發電第二期項目的CPT試驗和設計數據進行研究。以SBTn分類台灣西部海域之土壤，相較於SBT分類結果，大約在深度15m前整體由黏土區往砂土區移動的趨勢，但在15m後則呈現相反的趨勢。承載力結果顯示DCSBF-SM法與DCSBF-CPT法皆呈現較為不保守的趨勢，而ICP法較為保守。此外，UWA法與UCM法兩者趨勢相近。相較於SBTn土層，基於SBT的設計土層之極限承載力 (ICP法、UWA法與UCM法) 在淺層有放大但隨深度增加則趨向保守，且設計土層承載力甚至只有前者之半。

Offshore engineering commonly utilizes cone penetration tests (CPT) to obtain soil parameters. Therefore, data from the Cone Penetration Test (CPT) are often used as research parameters for soil classification or pile bearing capacity assessment in offshore engineering. However, the CPT-based soil classification results vary with different classification versions, and the corresponding pile bearing capacity also changes significantly. This article analyzes the axial bearing capacity of driven piles using the Design Code and Specifications of Building Foundations (DCSBF-SM method and DCSBF-CPT method), the ICP method, the UWA method, and the Unified CPT method (UCM method), with CPT test and design data of the second phase of Taiwan Power Company's offshore wind power project. Using the SBTn method to classify the soils in the western Taiwan offshore region, compared with the results from SBT method, the overall trend moves from clay zone to sand zone before the depth of 15m, but the opposite trend is shown after 15m. The results of the bearing capacity show that both the DCSBF-SM method and the DCSBF-CPT method exhibit relatively less conservative tendencies, while the ICP method is more conservative. Additionally, the UWA and UCM methods show similar trends. Compared to soil layers classified by SBTn, the ultimate bearing capacity (ICP method, UWA method and UCM method) of the design soil layer based on the SBT method is amplified in the shallow layer but tends to be conservative as the depth increases, and bearing capacity of design soil layer is even only half of that of the former.